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Cloning could make the genetic engineering of animals far less hit-or-miss.
Until now, most mammals could be modified only by injecting DNA into fertilised
eggs. The DNA would then integrate into the animal鈥檚 genome at random, with
uncertain results. A team led by Kenneth McCreath at PPL Therapeutics near
Edinburgh describes in this week鈥檚 Nature how they first grew adult
sheep cells in culture and made precise changes to targeted parts of the sheep
genome. Then they cloned the altered cells by fusing them with egg cells from
which the nuclei had been removed, and the cells grew into embryos. Out of the
80 embryos implanted, three lambs survived for more than six months. 鈥淕ene
targeting has only ever been done in mice before,鈥� says McCreath.